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AZT, the first drug that appears to curb the ravages of AIDS, was born of a bright idea that did not pan out.

It was the early 1960's, the era in the war on cancer when scientists were picking drugs off the shelf almost randomly to see if any might work. ''This approach was not at all intellectually gratifying,'' said Jerome P. Horwitz of the Michigan Cancer Foundation in Detroit, the man who first synthesized azidothymidine, or AZT. ''So we thought, how could we design a compound that would inhibit the duplication of cancer cells?''

From natural DNA, an essential component of all living matter, Dr. Horwitz and his colleagues manufactured a group of related compounds, dideoxythymidines, of which AZT was one. The drugs were akin to ''fraudulent nucleosides,'' he said. Nucleosides are the building blocks of DNA, and the researchers hoped that by inserting the artificial material into cells, the normal creation of DNA molecules would be hindered and that runaway growth of cancer cells would be impaired.

The scientists tested AZT and sister drugs in leukemic mice. ''We failed,'' Dr. Horwitz said by telephone on Thursday. ''The compound showed no activity.'' 'Waiting for the Right Disease'

Dr. Horwitz wrote up the dismal performance of his brainchild in 1964 and then turned to more promising subjects. ''My colleagues and I said that we had a very interesting set of compounds that were waiting for the right disease,'' he said.

''Then there was a long gap,'' saidSamuel Broder, director of cancer treatment at the National Cancer Institute in Bethesda, Md. But meanwhile, discoveries about a strange group of viruses, designated retroviruses, were laying the basis for today's glimmer of understanding of how the AIDS virus works and how to fight it.

The genetic instructions of retroviruses are in strands of RNA, another essential component of living matter, rather than DNA, the more familiar pattern. When a retrovirus invades a cell, it uses an enzyme, reverse transcriptase, to direct the formation of a DNA molecule.

By early 1984, only three years after the deadly new disease was discovered, French and American scientists had established that AIDS patients were infected with a retrovirus. The laboratory of Robert Gallo at the National Cancer Institute developed a means of producing large quantities of the AIDS virus and the search for weapons against it began in earnest. Joining Forces on AZT

Almost as soon as the cause of AIDS had been identified, researchers at the Burroughs Wellcome Company in North Carolina, which had considerable experience with drugs against herpes and other viruses, began testing chemicals that might be effective against retroviruses. AZT showed promise; Burroughs Wellcome, Federal agencies and universities worked together ''feverishly'' to bring AZT to where it is today, said Dr. David W. Barry, research director at Burroughs Wellcome.

Dr. Broder's laboratory in Bethesda had developed a system for rapidly screening potential weapons against the AIDS virus, tests using infected human cells that gave results in a matter of days. In early 1985, Burroughs Wellcome sent some AZT to the National Cancer Institute for testing, and also to laboratories at Duke University and the Food and Drug Administration.

According to Dr. Broder, the drug ''fools the virus into accepting these altered nucleosides into the growing chain of DNA.'' He added, ''Once that happens, the DNA chain gets terminated.''

Burroughs Wellcome quickly began testing the drug in animals and began discussions with the F.D.A., which took only a week to grant permission for human testing. On July 3, 1985, the first human patient, at the National Cancer Institute, received AZT. Early study of 19 patients showed that the drug harmed bone marrow at high doses but it was not seriously toxic; that it crossed into the brain, and, most important, that many recipients showed improvement in immunity and health.

Company officials said that last February they began collaborating with 12 different research centers to enroll 280 patients in a trial of the drug that was interrupted this week because those taking the drug did so well.

In Detroit, the creator of AZT, Dr. Horwitz, spoke this week of his pride in seeing once-frustrated work finally succeed. A new frustration lurks in the back of his mind: he never bothered to inquire about patents. ''If these chemicals provide a first generation of treatments against AIDS and leads for even better therapies, then our purpose will have been served,'' he said.

A version of this article appears in print on , Section 1, Page 7 of the National edition with the headline: A FAILURE LED TO DRUG AGAINST AIDS. Order Reprints | Today’s Paper | Subscribe